I can't prove it, but it has something to do with the fact that a drone doesn't have a father, but has a grandfather. and this repeats in sequence, since the grand father doesn't have a father. etc. etc.
But let's have a look about drones father at chromosome base.
1) Italian yellows have line and every emerged queen is yellow.
2) One beautifull day a virgin queen meets 10 yellow drones and 7 black drones.
3) Hive gets pure italians and crossed italian workers. Next summer hive makes 2 swarms and it needs 3 new queens for every colony.
4) By accident one is pure italians and 2 are crossed quite black queens.
5) When these queens make drones, and others are yellow and others quite black ones, we surely say that that crossed queens father was a black one. Difficult to say that grandfather was black.
6) The same fathers were fathers boath to queen and to drones. .. But are drones queen's stepbrothers or...?
But if someone does not know what means father, let's have a lesson about flowers and bees which hade one beautifull day a queen...a flight... and 2000 drones and of which 17 drones found same young queen ..and ..OR were they 17 grandfathers which ...